FreeDMO

Endless freedom for D.MO 550 series label writer printer.

<== Click here to download

Wiring

Components needed:

• 1 × STM32F103 bluepill
  search for: STM32F103 bluepill / STM32F103 bluepill with STLinkV2
  ::ATTENTION:: Make sure your blue pill is using the correct STM32F103C8T6. Some places sell blue pills with STM32F103C6T6 which are not compatible.

• 2 × cable
  search for: 6 pin 1.25 mm / 6pin 1.25mm Wire To Board Connector / JST GH 6pin

• 2 × resistor 4.7kΩ

Assembly

→ Make sure that the cables are connected correctly.
The left cable goes to the RFID board, the right cable goes to the main board of the label printer.

Attaching the RFID board is optional. If you only want to emulate one specific label type you don't have to connect the RFID board and 2 x 4k7Ω resistors.

STM32F103 blue pill:

Connection to RFID board:

Connection to main board:

Firmware

Option 1: Install the required ARM toolchain from distribution

• install the ARM toolchain from distribution (e.g. on Debian-based GNU/Linux install the gcc-arm-none-eabi and libnewlib-arm-none-eabi packages)

• run make to compile the firmware

Option 2: Install required ARM toolchain GNU Arm Embedded Toolchain from ARM:

• download and unpack from here: https://developer.arm.com/tools-and-software/open-source-software/developer-tools/gnu-toolchain/gnu-rm/downloads

• open the Makefile and modify the first line GCC_PATH to point to the GNU ARM embedded toolchain bin folder
  e.g. GCC_PATH = ../gcc-arm-none-eabi-10.3-2021.07

• run make to compile the firmware

Option 3: Use the precompiled firmware

• a precompiled firmware binaries are available here: Download

  You can choose one of the firmwares which has a default SKU for emulation (used when no real RFID tag is present)

Download the firmware to the STM32F103 bluepill board

• after compilation you can find the firmware file freedmo.bin in the build folder

• you can write the firmware via

  • SWD download using JLink-V2 and ST's JLink-Utility

  or

  • Serial download using an UART adapter and ST's FlashLoader Demonstrator
    This is the same procedure as downloading an USB bootloader to the bluepill board:
    https://www.electronicshub.org/how-to-upload-stm32f103c8t6-usb-bootloader
    Just select the file freedmo.bin in "Download from file" (2)

STM32CubeMx

The project comes with the CubeMX .ioc file which can be used to modify pins and/or change to different CPU types. The complete code is inside of ST's magic BEGIN_USER_CODE / END_USER_CODE markers so "Generate Code" in CubeMX can be used without any problems.

STM32F103 pin assignment

D.MO RFID tag emulation

After startup of the printer a default tag emulation is used which can be defined in the firmware. The emulation will count down correctly until the end of the roll is reached. A power cycle / sleep+wakeup of the printer is enough to reset the emulated tag counter back to it's maximum.

If the original RFID board is also connected and a spool with D.MO RFID tag is found then the emulation data is updated with the data from this RFID tag. Just the counter will be emulated in this case. This enables the use of any D.MO format unless you have at least one original spool (you can peel the RFID label of that role and attach it to the inside of the printer).

Please consider dumping this data and providing it here for others (see: https://github.com/free-dmo/free-dmo-tag-dump).

D.MO uses it's own Originality Signature (own signing key) which is used to sign the UID of the tag. This is used to only allow D.MO's own SLIX2 tags. However when you can emulate the UID you also can emulate the corresponding signature bytes, you just need to dump them from a valid tag.
(see: https://github.com/free-dmo/free-dmo-tag-dump).

The firmware contains some D.MO SLIX2 tag dumps which you can choose from:
file: Src/main.c

#define SLIX2_TAG_EMU 1
//#define SLIX2_TAG_EMU 2
//#define SLIX2_TAG_EMU 3

It does not matter which TAG_EMU you use. All of them will work for now. Maybe... in future D.MO will release new printer / firmware which might block those UIDs... but then we only need to dump a new spool of labels to get a new and valid UID+signature.

The data about the labels (SKU, size, count, ...) is encoded in the standard SLIX2 data blocks. Inside of this data is no dependency to the UID or signature. This enables a "mix and match" of SLIX2 tag (UID+signature) and the media data used from the printer. Unfortunately the encoded data uses an unknown CRC32 algorithm which limits us to use existing dumped label formats only.

You can choose from the list of included label data by selecting the SKU:
file: Src/main.c

#define DMO_SKU_S0722430 // 54 x 101 mm, 220 pcs.
//#define DMO_SKU_S0722550 // 19 x  51 mm, 500 pcs.
//#define DMO_SKU_S0722400 // 36 x  89 mm, 50 pcs.

Happy printing... 😈